The purpose of this project is to examine marrow and spleen grafts between adult mice with genetically defined antigenic differences to determine why some grafts succeed and to find which assays of donor-host compatibiliy best predict success of the marrow grafts. Erythrocyte-producing tissues of genetically anemic recipients are completely even when the donors have been specially bred to differ from the recipients at particular antigen-determining loci. No immune suppressive treatments are necessary although both marrow donors and recipients are immunologically competent adults. Successful grafts permanently cure the recipient's anemia. The growth of grafts can be quantitatively determined by following changes in blood values to normal levels. Marrow and spleen grafts from donors with genetically defined antigenic disparities will be given to anemic recipients. Many different donor-recipient combinations will be tested, and graft success will be compared with results from various compatibility assays to determine which assays best predict the donor-recipient combinations in which grafts will be successful. Successful grafts fail to mount graft-versus-host (GVH) reactions against even strongly incompatible anemic mice cured by the graft. The numbers, functional abilities, and locations of donor cells in immunolgical tissues of cured anemic recipients will be studied. Donors with different degrees of incompatibility will be compared. Measures to restrain GVH reactions in irradiated normal recipients will be attempted.